Most roll mills as utilized in the steel and aluminum industries employ an opposed pair of largediameter steel rollers which create a nip therebetween through which metal stock is fed so as to reduce its thickness, such as for forming plate or the like. The ends of these rolls have integral hubs of reduced diameter projecting outwardly therefrom, which hubs are supported in stands through antifriction or sleeve bearing assemblies. The metal stock which is fed between the rolls, whether it be aluminum or steel, is conventionally hot so as to effect rolling of the metal, and this high temperature of the metal coupled with the slag in the metal can cause excessive spauling of the roll surfaces. To increase the life of the roll surfaces, it is conventional to provide nozzles directly upstream of the nip so as to jet streams of cool water onto the hot metal. Such water effectively floods the metal and the nip area, and necessarily picks up substantial contaminates such as slag and the like. This coolant, however, also floods the areas surrounding the hub bearings. In an attempt to avoid contamination of the bearings, the bearings are conventionally provided with a seal arrangement such as a multiple lip seal disposed for sealing cooperation with the hub neck.
While assemblies of the above type using lip seal arrangements for sealing the hub neck have been utilized for many years, and in fact are still being utilized, nevertheless these lip seal arrangements have been unsatisfactory. For example, experience in this industry indicates that the lip seals create wear on the hubs and also rapidly break down so that the contaminate-containing coolant hence gains access to the bearings. The lubricant in the bearings hence rapidly deteriorates so that bearing seizure is a fairly common occurrence. In fact, it has been observed that bearing seizure sometimes occurs after a mill roll has been in use only a small number of hours. When bearing seizure occurs, it is necessary to shut down and disassemble the mill, and this is a costly endeavor. Removing the seized bearing from the hub of the mill roll is also difficult, and in many instances this results in breakage of the hub, or in the alternative the hub sometimes breaks at the time the bearing seizes. When this happens, the complete mill roll must be totally reworked as by being melted down and reformed. This is obviously expensive and time consuming as such mill rolls may cost as much as $50,000.00 each and a typical mill may have 12 sets of rolls each requiring four seals. In view of the magnitude of this problem, numerous types of seal assemblies have been utilized in an attempt to resolve the problem of contaminated coolant gaining access to the bearings, but most such attempts (involving various combinations of lip seals) have proven unsatisfactory in that they have not significantly increased the number of hours of operation prior to bearing failure.
Accordingly, this invention relates to an improved sealing arrangement designed specifically for protecting bearings of a mill roll, which sealing arrangement is believed to represent a significant departure from conventional sealing arrangements used for this purpose, and hence is believed to represent a significant improvement by permitting the mill to operate for significantly longer periods of time prior to experiencing bearing failure.
In the improved arrangement of this invention, there is provided an isolator assembly for cooperating between the hub neck and the support stand to isolate the bearing from the contaminated coolant. This isolator assembly includes a rotatable isolator ring (i.e. a rotor) which is nonrotatably coupled to the hub and is concentrically disposed between inner and outer non-rotatable isolator rings (i.e. stators). These isolator rings cooperate to define a clearance space therebetween which involves numerous close clearances including reversely oriented axial passages, and an enlarged annular collection chamber to permit trapping of the contaminated coolant due to centrifugal force, and removal of the coolant therefrom by centrifugal force prior to its reaching the bearing.
In the improvement of the invention, as foresaid, the arrangement of the isolator rotor with respect to the isolator stators is such as to reduce the energy of fluid flowing into the isolator so that gravity and centrifugal forces will trap the liquid and not allow it to flow into the bearing housing sump. To achieve this task, four features are provided, namely (1) a restriction of inward flow to reduce energy, (2) a change in fluid flow direction, (3) a radially outward pumping dam, and (4) a chamber to trap, dissipate energy and drain fluid contaminate to the atmosphere.
Other structural and operational advantages of the arrangement of this invention will be apparent after reading the following specification and inspecting the accompanying drawings.